StarDate Podcast

The star Regulus leads the Moon across the sky tonight. The bright heart of the lion is close to the upper right of the Moon at nightfall, with the gap increasing as the hours roll by. Regulus is about 79 light-years away. That means the light you see from Regulus tonight actually left the star about 79 years ago. So when a particle of light from Regulus hits your eye, it’s ending a journey of 79 years. As with many things astronomical, though, it’s all relative. For the particle of light itself – a photon – the trip took literally no time at all. That’s because the photon was traveling at the speed of light – 670 million miles per hour. Nothing can travel faster than that. And only photons can travel at that speed. That’s because photons have no mass – they weigh nothing at all. If anything else were to travel at lightspeed, it would become infinitely massive. So physical objects are limited to just below lightspeed. As an object moves faster, time appears to slow down for it as viewed by an outside observer – its clock would tick more slowly. So if you could accelerate a starship to just a fraction below lightspeed, it could travel for thousands of years as measured by a clock back on Earth – but just a few years or even less as measured by its own clock. So as you look at Regulus tonight, remember that the photons are completing a journey of both 79 years – and no time at all. Script by Damond Benningfield

A young planet is getting greedy. It’s gobbling up gas and dust from its surroundings. And observations last summer showed that its appetite got a lot bigger – it was consuming as much as eight times more material than in the spring. The planet is known by a catalog designation – Cha 1107. That indicates it’s in the constellation Chamaeleon, which is too far south to see from the United States. It’s hundreds of light-years away. Most planets are born in disks of material that encircle newborn stars. But this one appears to be on its own. That makes it a “rogue” world. It’s roughly five to ten times the mass of Jupiter, the largest planet in our own solar system, and about three times Jupiter’s diameter. It’s encircled by its own disk of material. That’s because it’s in a giant complex of gas and dust that’s giving birth to many new stars. As it pulls in material from its disk, it gets heavier – just like a newly forming star. The planet won’t get big enough to shine as a true star. But it’s possible that it could become a “failed” star known as a brown dwarf – a sort of missing link between stars and planets. Last summer’s outburst wasn’t the first for Cha 1107. It flared up in 2016 as well. So its growth process may be choppy – short feeding frenzies between longer periods of quieter appetite. Script by Damond Benningfield

If you’re looking for a world like Tatooine, good luck. Of the more than 6,000 known planets in other star systems, fewer than 20 orbit both stars of a binary system. So those double sunsets are few and far between. Just to refresh your memory, Tatooine is the home world of Luke Skywalker in Star Wars. Such planets are called “circumbinaries” because they circle around both stars in the system. Over the past decade, astronomers have searched for such worlds in a project with a rhythmic name: Bebop – Binaries Escorted by Orbiting Planets. The project looks for tiny “wiggles” in the motions of the stars caused by orbiting planets. It’s found a few planets, with several more candidates. One of those discoveries is Bebop-3b. The system’s two stars are quite close together. One of them is similar to the Sun. The other is only about a quarter of the Sun’s mass, and a tiny fraction of its brightness. The planet is about half the mass of Jupiter, the giant of our own solar system. It orbits the two stars once every 18 months, at a bit more than Earth’s distance to the Sun. We don’t know how fast Bebop-3b rotates, so we don’t know how often it sees sunrises and sunsets. All we know for sure is that there are two of each – one featuring a bright star, the other a faint cosmic ember. The system is about 400 light-years away. It’s high overhead at nightfall – but much too faint to see without a telescope. Script by Damond Benningfield

In the lexicon of astronomy, Pollux is known a class K-zero-3 star. That tells us that the star’s surface is a little cooler and redder than the Sun’s. It tells us that the star has puffed up to many times its original size. And it tells us that the star is nearing its end. Pollux is the brightest star of Gemini. It’s quite close to the Moon tonight. Its “twin,” the star Castor, and the brilliant planet Jupiter are a little farther from the Moon. The system that astronomers use to classify stars was developed more than a century ago. It groups the stars into classes O, B, A, F, G, K, and M. That system is based on a star’s surface temperature or color – hotter stars are bluer, while cooler stars are redder. O stars are blue-white, while M stars are red or orange. Each class is subdivided using the numbers zero through nine. At K-0, Pollux is just across the line from class G – the class that includes the Sun. The classification ends with the Roman numerals one through five. A “five” means the star is in the main phase of life. A “three” means it’s moved on to the giant phase. It’s converted the hydrogen in its core to helium. Pollux is now fusing the helium to make carbon and oxygen. That change has caused it to puff up; it’s nine times the diameter of the Sun. Over time, Pollux will get even bigger, cooler, and redder. It may evolve into class M – a brilliant star at the end of its life. Script by Damond Benningfield

Jupiter is the “big boy” of the solar system. It’s more than twice the mass of all the other planets combined. In many other star systems, though, Jupiter wouldn’t seem quite so impressive. Astronomers have discovered hundreds of planets that are heavier than Jupiter – up to 80 times Jupiter’s mass. Astronomers aren’t sure how such monster planets get to be so heavy. But they have a couple of main ideas. One says they grow from the mergers of smaller planets. The other says it depends on the environment in which a planet is born. Almost all planets take shape in disks of gas and dust around infant stars. The more material there is in the disk, the more there is for making planets. But there’s a limit on how massive a planet can become. Anything more than about 30 times the mass of Jupiter might become a brown dwarf – an intermediate step between planets and stars. And at more than 80 times Jupiter’s mass, it becomes a true star. The heavy planets don’t get much bigger than Jupiter, no matter how massive they are. As an object gains mass its gravity gets stronger. That squeezes it tighter, making it more compact. So while these “super-Jupiter” planets might outweigh Jupiter, they’d look a lot like the big boy of the solar system. Look for Jupiter near the Moon tonight. It looks like a brilliant star, so you can’t miss it. The twin stars of Gemini are close by, and we’ll have more about that tomorrow. Script by Damond Benningfield

Elnath has dual citizenship. Officially, it’s the second-brightest star of Taurus, so it’s known as Beta Tauri. It marks the tip of one of the bull’s horns. But it’s also known as Gamma Aurigae – one of the bright stars that outlines Auriga, the charioteer. That designation is un-official – it’s been considered defunct for almost a century. The dual identity is a result of changes in how astronomers define the constellations. At first, the constellations were vaguely defined. Each one encompassed the connect-the-dots pattern that outlined the classical figure. But there weren’t hard borders. In 1603, German astronomer Johannes Bayer published a new naming scheme for all the stars. In it, he assigned Elnath to both Taurus and Auriga. That worked fine for centuries. But in the early 20th century, astronomers decided to assign precise boundaries for each constellation – like the borders of states or nations. Elnath was just inside the border of Taurus. So, officially, Elnath belongs to the bull. But it still forms part of the classical outline of Auriga – giving Elnath a dual citizenship. Elnath is about 130 light-years away. It’s about five times the size and mass of the Sun, and it’s hundreds of times brighter. It’s easy to pick out tonight because it’s close to the Moon. As night falls, they’re no more than one or two degrees apart – right along the border between the bull and the charioteer. Script by Damond Benningfield

Just about every star is born in a cluster – a family of dozens to thousands of stars. Most of these families fall apart, with the individual stars going their own way. The Sun’s cluster, for example, dissipated billions of years ago. One cluster that’s in the process of dissipating is the Hyades, which outlines the face of Taurus, the bull. It’s the nearest cluster, at a distance of about 150 light-years. Today, the Hyades contains several hundred stars – probably less than half its original population. The other stars were pulled away by the gravitational tug of the rest of the galaxy. The cluster’s heaviest stars reside in its tightly packed center. None of them is much more than about twice as massive as the Sun. That’s because of the cluster’s age – 625 million years. All of its heavier stars have already burned out. All that remains is their dead cores. The least-massive stars have migrated to the outskirts of the cluster. Over the next few hundred million years, those stars will all drift away. That will leave only a sad little remnant of this impressive family of stars. The Hyades stands to the lower left of the Moon this evening. Its stars form a “V” shape. The brightest star in the outline is bright orange Aldebaran, the bull’s eye. But it’s not a member of the cluster – it simply lines up in the same direction as the stars of the Hyades. We’ll have more about the Moon and Taurus tomorrow. Script by Damond Benningfield

For the kings of ancient Egypt, the Sun was much more than just a glowing orb in the daytime sky. It was the god Ra, one of the most important of all the gods. Ra was a creator of life, the king’s father, and a representation of the king as a god himself. So the kings of the Fifth Kingdom, about 4500 years ago, built temples to honor the Sun. Archaeologists have recently excavated about half of the largest one yet discovered – a massive complex that might have been topped by a spot for watching the Sun and stars. The temple is named “Joy of Ra” or “Joy of the Heart of Ra.” It’s at Abu Gorab, about 10 miles from Cairo, near the ancient capital, Memphis. It was built by King Nyuserre, who reigned for two or three decades. At the time, the kings identified themselves with Ra – as eternal gods. So the temple was a place to honor both Ra and the king. Excavations have uncovered two large enclosures. The upper level was discovered 125 years ago, but the lower one was found just recently. The upper level included an altar for making offerings to Ra. And one end featured an obelisk that would have towered high above the courtyard and the surrounding landscape. It had a perfect east-west alignment – the directions of the rising and setting Sun. The recent work also uncovered a stairway to the roof. The rooftop probably served as an observatory – helping Nyuserre follow his “father” across the sky. Script by Damond Benningfield

An astronomer greets visitors to a science museum in Canberra, Australia. He’s made of riveted iron plates, and he stands atop a wide ring, gazing skyward through a smaller ring in his right hand. He’s the last remnant of an historic telescope that was destroyed in a massive wildfire. The fire blazed across Australia in January of 2003. It destroyed most of Mount Stromlo Observatory, one of the major astronomy research centers in the southern hemisphere. The fire consumed five telescopes, plus a laboratory where scientists and engineers built astronomical instruments. One of the casualties was the Yale-Columbia Telescope. It was a 26-inch refractor – a type of telescope that uses lenses to gather and focus starlight. It was built in 1924, and had been operating at Mount Stromlo for half a century. Astronomers had used it to measure the distances to stars, to study double stars, and more. After the fire, an Australian science institute commissioned a sculptor, Tim Wetherell, to create an artwork from the telescope’s remains. The result was “The Astronomer” – the piece on display in Canberra. The figure stands on a setting circle – a wide ring that indicated where the telescope was pointing. It has numbers at 10-degree intervals, from zero to 180. The astronomer is holding a smaller version of the ring in his hand – continuing to look at the stars long after the telescope’s demise. Script by Damond Benningfield

The crescent Moon and the planet Venus team up in the evening twilight tonight. Venus is the brilliant “evening star.” It’s below the Moon, and it sets by the time the sky gets fully dark. Venus is enveloped by an unbroken layer of clouds – one of the reasons the planet looks so bright. The clouds are a few dozen miles above the surface. And they’re speedy – they race around the planet at up to 335 miles per hour – twice as fast as the winds in a category-5 hurricane. They make a full turn around Venus every four days. That’s more than 50 times faster than the planet is turning on its axis. That high-speed motion is called super-rotation. No one knows for sure what causes it. A study a few years ago said it might be powered by the Sun. The clouds are hottest at the equator, where the sunlight is strongest. The hotter atmosphere flows outward, toward the poles and toward the nightside – reaching super-fast speeds. Super-rotation doesn’t extend all the way to the surface, though. Below the clouds, the wind speed drops dramatically. At the surface, there’s almost no wind at all. But the atmosphere is quite dense – more than 90 times the density of Earth’s atmosphere. Any wind at all exerts a lot of pressure, so it can erode the surface. That can wear away mountains, and gouge channels that look like they were carved by flowing water – all below the speedy clouds of the planet Venus. Script by Damond Benningfield

A galaxy cluster is like a cosmic blender. It stirs up the galaxies and the space between them. Nothing is left undisturbed. A perfect example is the Virgo Cluster. It consists of more than 1500 individual galaxies, centered about 55 million light-years away. Most of them are fairly small and faint. But a few are monsters – many times the size and mass of our home galaxy, the Milky Way. The cluster’s galaxies are packed fairly close together. So the gravity of each galaxy pulls at its neighbors. That distorts the shape of some of the neighbors, making them lopsided. It also causes big clouds of gas to collapse and give birth to new stars. And it pulls many stars out of the galaxies, into the space between them. In fact, up to one-tenth of the stars in the cluster may be roaming through intergalactic space. The cluster’s brightest galaxy is Messier 49. It was the first to be discovered, in 1771. It’s a giant elliptical, so it looks like a fat, fuzzy rugby ball. It’s much bigger than the Milky Way, and many times its mass. And a supermassive black hole inhabits its heart. The biggest and heaviest member of the cluster is Messier 87, and we’ll talk about it tomorrow. The Virgo Cluster is centered along the border between Virgo and Leo. That spot is low in the east at nightfall and climbs high across the sky later on. Many of the galaxies are easy targets for small telescopes. Script by Damond Benningfield

Snow blanketed the launch pad, and the rocketeers sipped hot malted milk to ward off the chill. But the launch they conducted a century ago today turned the idea of space travel from fantasy to possibility – and provided the first small step toward the Moon. The rocket was designed by Robert Goddard, a physics professor at Clark University in Massachusetts. Goddard was brilliant but secretive. He refused to collaborate with other scientists, and seldom even talked about his research. Instead, he spent his time building, testing, and flying rockets. At the time he started, all rockets were powered by solid fuels, such as gunpowder. But solid fuels are inefficient and hard to control. So Goddard built a rocket powered by liquid fuels – gasoline and liquid oxygen. It was a potent mixture that provided far more energy per pound than solids. Goddard and his wife and assistants launched the first liquid-fueled rocket in history on March 16th, 1926. It was airborne for just two and a half seconds, and climbed just 41 feet. But it proved that liquid fuels could propel a rocket skyward. Goddard spent two more decades experimenting with rockets. German engineers used many of his innovations in the V-2, which bombarded England during World War II. Transplanted to the United States after the war, many of these engineers developed the rockets that boosted satellites into space – and sent astronauts to the Moon. Script by Damond Benningfield

A three-way tug-of-war isn’t a common sight – unless you look toward the constellation Leo. Three galaxies there are tugging at one another, producing some spectacular results. The galaxies are M65, M66, and NGC 3628 – the Leo Triplet. All three galaxies are about the same size as our home galaxy, the Milky Way. And each may resemble the Milky Way – a beautiful spiral with a long “bar” of stars across its middle. The triplets are close enough together that the gravity of each galaxy exerts a strong pull on the others. That’s given M66 a slightly “wonky” look. The galaxy’s core is a little off-center. Its spiral arms are loosely wound, and they aren’t symmetrical. And the arms are lined with knots of starbirth. Some of the stars in these regions are huge. Such a star burns out quickly, then explodes as a supernova. And since 1973, we’ve seen five supernovas in M66 – compared to zero in the Milky Way. We see NGC 3628 edge-on, so it’s hard to know its exact shape. What we do see is a lane of dark dust sandwiched between brighter layers. We also see a “tail” that’s 300,000 light-years long – three times the size of the galaxy itself. It’s a ribbon of stars pulled out by the other galaxies in their ongoing “tug-of-war.” Leo is in the east at nightfall. The triplet is to the upper right of Denebola, the star at the lion’s tail. It’s an easy target for a small telescope. Script by Damond Benningfield

It sounds like a toddler’s attempt to say “Friday” or, even better, a day to gorge on apple crumb or coconut cream. Alas, “Pi Day” is something completely different. It’s a commemoration of a mathematical constant that’s represented by the Greek letter pi – one of the most important quantities in science. Pi is the ratio of a circle’s diameter to its circumference. When it’s rounded off to two digits, it’s 3.14 – the numerical equivalent of March 14th. Astronomers use pi to calculate the volume and density of a star or planet, the details of an orbit, and much more. Other scientists use it as well. But pi is an “irrational” number. That means that no matter how long you calculate its exact value, you never reach the end – whether you go to a thousand decimal places, a million, or rbrm eleventy-jillion. There’s never a conclusion, and no group of numbers ever repeats. Mathematicians have used various techniques to try to calculate the exact value, without success. The record so far is more than a hundred trillion places to the right of the decimal. Trying to calculate an exact value has been an important plot point in science fiction. Any time a computer is getting too uppity, it’s commanded to calculate pi to the last digit. That impossible task overloads the computer, allowing the heroes to regain control. Whether we’ll need it to rein in A-I – well, have a slice of pie – the tasty variety – while you ponder it. Script by Damond Benningfield

To the eye alone, the brightest star in the night sky is Sirius, the leading light of Canis Major, the big dog. It’s well up in the south at nightfall – a brilliant beacon less than nine light-years away. If we could shift the sensitivity of our eyes to shorter wavelengths, the brightest star would appear a little below Sirius. Adhara is already the second-brightest star in the constellation. But it produces most of its energy in the extreme ultraviolet – wavelengths that are far too short to see with the human eye. At those wavelengths, Adhara would be the brightest object in the entire night sky. The star is an ultraviolet powerhouse because it’s tens of thousands of degrees hotter than the Sun. The hotter an object, the more U-V it produces. And Adhara is huge – more than 10 times the Sun’s diameter. So there’s a lot of real estate for beaming its radiation into space. The U-V zaps molecules of gas and dust anywhere close to the star, splitting them apart and making them glow. But the star has been around long enough that it’s already cleared out most of the space around it. More than four million years ago, Adhara was much closer to the Sun than it is today. That made it the brightest star at visible wavelengths as well. It shined as brightly as Venus, the morning or evening star. But Adhara’s motion through the galaxy has carried the star much farther from us – allowing Sirius to outshine this sizzling star. Script by Damond Benningfield

For Charles Messier, star clusters were a nuisance. The French astronomer was mainly interested in comets. In the 18th century, finding a comet could bring fame and fortune – kings sometimes awarded medals and fat stipends for their discovery. Through a telescope, star clusters could resemble comets. Messier and others might spend time following a cluster, only to find out that it wasn’t the prize. So Messier compiled a catalog of clusters and similar nuisances – a list of objects to ignore. Four of the clusters follow a narrow path near Canis Major, the big dog: M46, 47, 48, and 50 – a Messier “highway.” Although they’re close together in our sky, the clusters are not close together in space. Their distances range from about 1600 light-years to more than five thousand. So there’s no relationship among them. They appear close together because they all lie along the Milky Way – the glowing outline of the disk of the Milky Way Galaxy. In that direction, we’re looking into the most densely populated region of the galaxy, so we see many more stars and star clusters – including the “pesky” clusters cataloged by Charles Messier. The clusters are in the southeastern quadrant of the sky as night falls. Look for Sirius, the brightest star in the night sky, due south. The clusters spread out to the left and upper left of Sirius. All of them are easy targets for binoculars. Script by Damond Benningfield

Winter brings out the big dogs – some of the most prominent constellations of all. And one of those really is a dog: Canis Major, the big dog. It’s best known for Sirius, the Dog Star – the brightest star in the night sky. It’s a third of the way up the southern sky at nightfall. But there’s much more to Canis Major than just Sirius. It includes several bright stars, most of which are below or to the right of Sirius. When you link them up, they do form the outline of a dog. Like all constellations, Canis Major consists of more than just a connect-the-dots pattern of stars, though. It covers a patch of sky that includes everything within its borders. And in that area, you can find several deep-sky objects – objects like star clusters, which are far beyond most of the individual stars visible in Canis Major. Perhaps the best known is Messier 41. It’s not far below Sirius, and it’s an easy target for binoculars. It’s about 2300 light-years away, and includes a hundred or more stars. The cluster probably is about 200 million years old. At that age, its biggest, heaviest stars have expired. They’ve left behind small, dense corpses known as white dwarfs. The next-heaviest stars soon will follow the same path. Those stars have puffed up to become red giants. They’re easily visible through binoculars – sparkling red and orange jewels along the “collar” of the big dog. More about Canis Major tomorrow. Script by Damond Benningfield

A magazine that first hit newsstands 100 years ago today was unlike anything readers had seen before. Its cover featured a brightly-colored painting of people ice-skating on a comet as it zoomed past Saturn. Its founding editor, Hugo Gernsback, called it “a new sort of magazine” – “a magazine of ‘scientifiction'” – a genre known today as science fiction. Amazing Stories was the first magazine dedicated solely to the genre. Its debut issue, which was dated April 1926, carried reprints of stories by Jules Verne, H.G. Wells, Edgar Allen Poe, and others. The story titles included “The Man from the Atom” and “The Thing from – Beyond.” The magazine was an instant hit. Within a year, monthly circulation was at 150,000. Other publishers quickly caught on, and began publishing many more sci-fi magazines. Over the decades, they included such titles as Fantastic, Astonishing, and Astounding. They featured many of the major figures of science fiction’s “golden age.” Their inventive stories and eye-catching covers caught the attention of lots of youngsters. The magazines inspired many of them to pursue careers in astronomy, physics, engineering, and related fields. They also inspired future filmmakers, who expanded “scientifiction” far beyond the printed page. Few science-fiction magazines have survived. But their influence is still felt today – on Earth – and beyond. Script by Damond Benningfield

A future super-giant “onion” perches close to the Moon at dawn tomorrow. It’s the star Antares, the bright heart of the scorpion – one of the most impressive stars in the galaxy. Antares is a supergiant. It’s roughly a dozen times as massive as the Sun, and hundreds of times wider. Because it’s so heavy, gravity squeezes its core tightly. That revs up the nuclear fusion in the core. Like all stars, those reactions initially fused hydrogen to make helium. In the Sun, hydrogen fusion will last about 10 billion years. In Antares, though, it lasted a little more than 10 million years. When the hydrogen in the core was gone, the core shrank, making it hotter – hot enough for the helium to fuse to make carbon and oxygen. That process will last about one million years. Then the carbon will fuse to make heavier elements, and so on. Each step takes less time than the one before. In the final step, silicon will fuse to make iron – a step that takes just a few days. The lighter elements won’t all go away, though. Instead, the “ash” from each step will form layers around the core – like an onion. But that structure won’t last. The core can’t get hot enough to fuse the iron. Gravity will win out, and the core will collapse – forming an ultra-dense neutron star. Everything outside the core will blast outward at a few percent of the speed of light. Supergiant Antares will explode as a supernova – an impressive end for an impressive star. Script by Damond Benningfield

Canopus would be a terrible neighbor. The star is big, bright, and hot, so it might blow away any planet-making materials around nearby stars. Even worse, it may be destined to explode. That would zap any existing planets with radiation – perhaps endangering any life in nearby star systems. Canopus is the second-brightest star in the night sky. At this time of year, it’s visible from the southern third of the United States in early evening. It’s low in the south, well below Sirius, the brightest star. Canopus is at least eight times the mass of the Sun. So even though it’s billions of years younger than the Sun, it’s already completed the main phase of life. Within a few million years, its core will collapse, perhaps forming an ultra-dense neutron star. If so, then its outer layers will blast into space as a supernova. Such an outburst would produce enormous amounts of X-rays and gamma rays – the most powerful forms of energy. That could strip away the ozone layer of any planet within a few dozen light-years, subjecting the surface to high levels of radiation. So far, we know of only one planet within that range where conditions are most suitable for life. The planet itself isn’t likely to host life. But any big moons might be more comfortable homes – at least until the demise of Canopus. Luckily for us, Canopus is 300 light-years away. So Earth is well outside the “danger zone” of this not-so-neighborly neighbor. Script by Damond Benningfield

The tale of Jason and the Argonauts is one of the biggest and boldest stories in Greek mythology. And it involves some of the greatest heroes, many of whom are depicted in the stars – from the twins of Gemini to mighty Hercules. The boat itself was placed in the stars as well. But even it was too big. Astronomers eventually split it apart. The original constellation was Argo Navis. It was first drawn almost 3,000 years ago. It was far larger than any of the other ancient western constellations. And for a long time, that was just fine. But as astronomers began studying the stars with telescopes, the Argo was just too big – there were too many stars and other objects within its borders to catalog. In 1756, French astronomer Nicolas Louis de Lacaille decided to do something about it. He split the Argo apart. He kept the references to the boat, though. So his new constellations were Carina, the keel; Vela, the sail; and Puppis, the poop deck – the deck at the back of the boat. And those constellations are still in use today. Carina is best known for its brightest star, Canopus. It’s the second-brightest star in the night sky. And from the southern latitudes of the United States, it crawls low across the south in early evening at this time of year. As night falls, it’s just above the horizon, almost directly below Sirius, the brightest nighttime star. We’ll have more about Canopus tomorrow. Script by Damond Benningfield

The first ship in a solar-system armada reached its target 40 years ago today. Over the following week, four others joined it. Their target was Comet Halley. It was making its first passage through the inner solar system since 1910. So it was the first chance to study the comet from close range. And space agencies around the world responded. The Soviet Union and Japan each sent two spacecraft, and Europe added one more. The first to arrive was Vega 1, one of the Soviet missions. It and a companion, Vega 2, had first flown past Venus. They scanned the planet and dropped probes into its atmosphere. Both of them flew just a few thousand miles from Halley’s nucleus – its “body” of rock and ice. Europe’s contribution, Giotto, came even closer – just 370 miles. It snapped by far the best pictures of any comet. It found that most of the nucleus was covered by a “crust” that was darker than charcoal. But “jets” of ice and dust erupted from thin spots in the crust. They wrapped the nucleus in a cloud of debris. Sunlight and the solar wind pushed some of that material away from the comet, forming a tail that was millions of miles long. The United States was a notable no-show. A dedicated mission to Halley was scuttled. NASA did turn some craft that were already in space to face Halley, but they were millions of miles away. The next chance to study the comet up close won’t come until 2061. Script by Damond Benningfield

Visitors sometimes just drop in on us. But a visitor to a home in Georgia took the notion of “dropping in” a bit far. It smashed through the roof, an air duct, and a thick layer of insulation before splatting into the floor, leaving a crater the size of a quarter. It missed smacking into a resident by just 14 feet. The “visitor” was a meteorite – part of a much larger space rock. The rock formed a glowing streak as it raced through the skies of the southeastern United States on June 26th. Hundreds of people saw it, and many more heard it – it produced a sonic boom, plus an explosion before it hit the ground. The bit that smashed into the house was one of more than 200 samples recovered. In all, they totaled about 12 pounds. Collectively, they were called the McDonough meteorite for the small town where they hit. Eyewitness reports, videos, weather radar, and weather satellites helped scientists reconstruct the space rock’s origin. It came from the asteroid belt – a wide band of debris between the orbits of Mars and Jupiter. It probably was a piece from a much larger body that broke apart 470 million years ago. Lab studies revealed the meteorite’s age: 4.56 billion years – about 20 million years older than Earth. That means it was similar to the rocky building blocks that came together to make Earth. So the McDonough meteorite is an ancient visitor that dropped in with a bang. Script by Damond Benningfield

Last July, a space telescope heard the death cry of a star billions of light-years away. It was the longest outcry of its type ever detected – an astonishing seven hours. Yet its details are still fuzzy. All we know for sure is that it was a violent ending for a star. The outcry was a gamma-ray burst. Astronomers have discovered thousands of them. They’re usually produced by a supernova – the titanic explosion of a massive star. Energy from the nuclear inferno deep inside the star blasts outward through its poles. That forms narrow jets of gamma rays – the most powerful form of energy. The gamma rays usually last a few seconds or minutes. In that time, though, the burst can emit more energy than the Sun will produce over billions of years. Follow-up observations showed that the July outburst took place in a galaxy that’s giving birth to many stars – perhaps as the result of a merger with another galaxy. Many of the new stars are hot and massive, so they explode quickly. That makes the galaxy a good breeding ground for gamma-ray bursts. But the origin of this event isn’t clear. It could have been the result of a supernova. Other possible scenarios include the merger of a black hole with the dead or stripped core of a Sun-like star, or a close encounter between a star and a mid-sized black hole. Such an encounter would have ripped the star apart, forming a trail of incandescent gas – triggering a long outcry from a dying star. Script by Damond Benningfield

Two of the planets of the solar system are crossing paths in the early evening. But they’re quite low in the sky, so they can be a bit tough to spot. The brighter of the two is Venus, which is beginning its reign as the “evening star.” It’ll climb higher into the sky over the coming weeks and months, making it much easier to spot. Right now, though, it sets by the time the color of twilight drains away, so there’s not much time to enjoy it. Venus’s companion is Saturn. It’s close to the upper left of Venus. It’s only about one percent as bright, so it’s tougher to pluck from the twilight. You might miss it entirely if not for the presence of its brighter sibling. And the two planets really are siblings. They were born from the same cloud of gas and dust that surrounded the newborn Sun. Venus was born close to the Sun. Conditions in that region were so hot that only heavier materials were available to build planets. So, like Earth, Venus is made mostly of rock and metal. Saturn took shape in the deep-freeze of the outer solar system. The planet built a big core of heavy materials. The core then pulled in huge amounts of gas. That made Saturn the second-largest planet – a cold, gassy world far from the Sun. Watch Venus and Saturn as they cross paths the next few nights. They’ll stand side by side on Saturday, just a whisker apart. Venus will pull away after that, with Saturn vanishing in the sunlight. Script by Damond Benningfield

Life is all about cycles: birth and death, the rise and fall of the seasons, Taylor Swift tour eras. Many cycles play out in the sky as well. One of them is in view in the wee hours of tomorrow morning, as the Moon and Sun stage a total lunar eclipse. All or most of it will be visible across most of the United States. A lunar eclipse occurs when the Moon passes through Earth’s long shadow. The Moon’s orbit is tilted a bit, so most months the Moon passes above or below the shadow. When the geometry is just right, though, it plunges through this cone of darkness. Each eclipse is part of a centuries-long cycle, known as a Saros. Individual eclipses in a Saros are separated by about 18 years. Tonight’s eclipse is the 27th of 71 eclipses in this cycle. The previous eclipse in the cycle took place in 2008, with the next in March of 2044. But several Saros cycles are unspooling at the same time, so Earth sees two or more lunar eclipses every year. Totality – when the Moon is fully immersed in the shadow – will last about 58 minutes. Alaska, Hawaii, and much of the West Coast will see the entire eclipse sequence. That includes the partial phases, as the Moon moves into and out of the shadow. Much of the rest of the country will see all of the total eclipse, and most of the partial phases, with the Moon setting before the eclipse ends. Script by Damond Benningfield

The Moon stalks the heart of the lion tonight. And seen from Hawaii, it’ll catch it. The Moon will “occult” the heart, blocking it from view. The lion’s heart is Regulus, the brightest star of Leo. The name Regulus means “the little king.” It was introduced 500 years ago. But the star’s association with royalty goes back much farther. In ancient Persia, Regulus was one of the four “royal” stars – four especially bright stars near the ecliptic – the Sun’s path across the sky. The stars are roughly evenly spaced around the ecliptic. That means each star is at its best during a different season. So each star was considered the “guardian” of its season. Regulus is closer to the ecliptic than the other three guardians, so it was the most important of them all – a king among kings. The Moon stays close to the ecliptic as well, straying only a few degrees to either side. So it circles past the same stars every month – including Regulus. Right now, the Moon’s path carries it especially close. And that’s easy to see tonight. Regulus is below the Moon as night falls. But as the hours roll by, the Moon will creep closer and closer to the bright star. As seen from the continental United States, they’ll be separated by no more than about one degree as they set, before dawn – the width of a pencil held at arm’s length. And from Hawaii, the Moon will catch the star – “eclipsing” the little king. Script by Damond Benningfield

The planets in our solar system fit into two groups. Four of the planets are small and rocky; Earth is the largest. The other four are big and bloated; Neptune is the smallest. But there’s nothing between the sizes of Earth and Neptune. And that’s a bit odd. Two of the most common types of planets elsewhere in the galaxy are somewhere in the middle: super-Earths and mini-Neptunes. Astronomers have confirmed more than 6,000 planets in other star systems. Only one system has as many known planets as the solar system does. And the planets in almost all the known systems are packed in much closer to their stars than the worlds of the solar system – in part because close-in planets are the easiest to find. But the biggest difference between our system and all the others appears to be the lack of super-Earths and mini-Neptunes. A super-Earth is up to twice the diameter of Earth, and two to ten times Earth’s mass. Such worlds probably are dense and rocky. They may have thick atmospheres of hydrogen and helium, and perhaps deep oceans of liquid water. Mini-Neptunes are larger than super-Earths, but no bigger than Neptune. They probably have a solid core as well, but thicker layers of gases and liquids. The distinction between the two types of planets isn’t always clear. They probably have a lot in common – including the fact that we don’t have either of them in our own solar system. Script by Damond Benningfield

You might forgive Pollux if it feels disrespected. It’s the brightest star of Gemini – twice as bright as Castor, its “twin.” But the designation that’s most often used by astronomers is Beta Geminorum. And the Greek letter “Beta” usually is applied to a constellation’s runner-up. That naming system was created by German astronomer Johann Bayer, in 1603. He used the Greek alphabet to name most of the stars in a constellation. Usually, the brightest star was given the first letter, Alpha. The next-brightest was Beta, and so on. But in some cases, Bayer switched things up. He labeled the stars based on their location in the constellation’s classical outline, or on some other category. So for Gemini, Pollux became the “Beta” star even though it’s clearly brighter than “Alpha.” Pollux really is an impressive star. It’s moved into the red-giant phase of life. In fact, it’s the closest red giant to the Sun, at a distance of just 34 light-years. It’s puffed up to about nine times the diameter of the Sun, so it shines almost 40 times brighter than the Sun. And it has a distinctively orange tint – a beautiful look for an impressive star. Pollux and Castor line up to the upper left of the Moon at nightfall this evening. Pollux is closer to the Moon. The planet Jupiter is farther to the upper right of the Moon. Jupiter outshines all the true stars in the night sky – even the brightest light of Gemini. Script by Damond Benningfield

If you head for orbit around Jupiter, you might want to take along your dust mop. Wide but thin rings encircle the planet. And they’re made of tiny particles of dust. Jupiter’s rings are nothing like the magnificent set that encircles Saturn. The rings are so faint, in fact, that they weren’t discovered until 1979, when the Voyager 1 spacecraft flew close to Jupiter. The system consists of four main rings. The inner ring, known as the halo, contains especially tiny particles, like a thin haze. The particles in the main ring are a little larger, but still quite small. And the two outer rings – known as gossamer rings – are wide and thick, but still don’t add up to much. The particles that make up the rings probably were chipped off of some the small moons that orbit close to Jupiter. Chunks of ice and rock slam into the moons, blasting out clouds of debris. The particles in the rings spiral into Jupiter quickly – within hundreds or thousands of years. So the rings are being constantly replenished by more impacts – adding to the dusty environment around the solar system’s largest planet. Jupiter teams up with the Moon and the twins of Gemini tonight. The planet looks like a brilliant star below the Moon at nightfall. It’s far brighter than any of the true stars. Gemini’s twins – the stars Castor and Pollux – line up to the lower left of the Moon. More about this beautiful grouping tomorrow. Script by Damond Benningfield

The first solar flare ever observed was also by far the biggest yet seen. But such a monster storm will happen again. And when it does, it’s unlikely that even a single spacecraft in Earth orbit will come out unscathed. And many could be destroyed. The benchmark storm so far was the Carrington Event. It was observed by British astronomer Richard Carrington, in 1859. He saw a brilliant flash of light erupt from a dark sunspot. The eruption produced beautiful displays of the northern and southern lights. It also zapped telegraph wires, disrupting transmissions and even starting fires in some stations. Scientists at the European Space Agency recently simulated what would happen to satellites if such a monster storm hit us today. They concluded that it would be bad – really bad. Over a period of about a day, GPS systems would fail. Satellite instruments would glitch or fail, entire satellites would be destroyed, and some ground stations would be knocked out. Earth’s outer atmosphere would expand dramatically, dragging satellites down. That would increase the risk of collisions, and reduce the time in orbit for any survivors. Operators can take some actions to protect their satellites. But that requires good forecasts of space weather. And future satellites could be equipped with better shielding. Even with those precautions, though, no satellite would be unaffected by the fury of a monster storm on the Sun. Script by Damond Benningfield

Anything that’s in Earth orbit faces the constant threat of radiation – energy and charged particles from the Sun and beyond. It can cause instruments to glitch or fail, and even destroy a satellite. And it poses a health risk for astronauts. The threat is greatest in a zone in the southern hemisphere – the South Atlantic Anomaly. It covers several million square miles above South America and South Atlantic Ocean. It’s a weak spot in Earth’s magnetic field that allows intense radiation to penetrate closer to the surface. And it’s getting bigger. The magnetic field can deflect many of the charged particles that bombard our planet. That protects orbiting satellites and astronauts. It also protects the surface from power blackouts and other effects. But the field is offset a bit from the center of the planet. It extends a little farther into space in some regions, but dips closer to the surface in others. And the South Atlantic Anomaly is the biggest dip of all. Spacecraft that are passing through the region often have to switch off some of their instruments to protect them from the harsh radiation. A recent study found that the anomaly has gotten bigger over the past decade – by about half the area of continental Europe. So the space above that part of Earth is getting nastier – a bigger “danger zone” in the southern hemisphere. We’ll have more about radiation hazards tomorrow. Script by Damond Benningfield

To the eye alone, the Pleiades cluster looks like a small dipper of about seven stars – a few more if you have nice, dark skies. But when Galileo Galilei looked at it with his first small telescope, he saw a few dozen stars. It was one of the first indications that there’s far more to the universe than meets the eye. You can share Galileo’s view with a basic pair of binoculars – no telescope required. They’re especially helpful tonight because of the Moon. It passes through the outskirts of the cluster, so it points the way. But the moonlight makes it tougher to see the stars. The Pleiades is a family of perhaps a couple of thousand stars. The stars were all born together, from the same cloud of gas and dust. That makes the cluster a good laboratory. Since the stars all started with the same mix of elements, any differences among them are the result of their evolution – changes within the stars themselves. That helps astronomers understand how all stars change over the eons. The cluster probably is a little more than a hundred million years old. That means it’s completed only about half an orbit around the center of the galaxy. During that time, it’s lost many of its original stars. And before it can complete one full orbit from its current location, it’s likely to evaporate – pulled apart by the gravitational tug of the rest of the galaxy. Tomorrow: a growing “danger zone.” Script by Damond Benningfield

Stars aren’t always nice to their offspring – especially at the end. As a star dies, it expands. It can get big enough to engulf some of its planets. The Sun, for example, is likely to swallow Mercury and Venus, and might get Earth as well. A star in Cygnus might have engulfed one of its planets fairly recently. Two others might be doomed as well. Kepler-56 isa red giant – a dying star that’s much bigger than the Sun. It has three known giant planets. Two of them are quite close in, so they may not survive the star’s final act. Kepler-56 is rotating much faster than most red giants. And vibrations at the surface reveal that its core and its outer layers are spinning at different rates and angles. There are several possible reasons for this odd behavior. One is the gravitational influence of the close-in planets. Another is that the star might have swallowed a planet early on. A recent study suggested something else: The star might have swallowed a planet fairly recently. The planet would have been about as massive as Jupiter, the giant of our own solar system. As it plunged in, its orbital momentum spun the star up. So Kepler-56 isn’t being kind to its offspring as its own life comes to an end. Kepler-56 is in the east-northeast at dawn. It’s half way between Deneb, Cygnus’s brightest star, and even brighter Vega. But Kepler-56 is too faint to see without a telescope. Script by Damond Benningfield

Things sometimes flash in the night sky. That includes some weird and wonderful astronomical objects. Some of them shine for a few minutes or even seconds, then vanish. So it can be tough to understand just what caused them. Thousands of these “transients” showed up in a decade-long look at the night sky. And a recent study found a statistical link between some of those transients and both nuclear weapons tests and reports of UFOs. The study analyzed thousands of nights of observations by the Palomar Sky Survey. From 1949 to 1958, astronomers repeatedly photographed the night sky on glass plates, looking to compile the best map of the heavens to date. Many of the plates revealed transients that were star-like pinpoints of light. They appeared out of nowhere, then disappeared just as quickly. The study found that, on average, the number of transients was greater on nights just after above-ground nuclear explosions. And there were more reports of UFOs on nights with more transients. There are many possible explanations. There could be problems with the original plates, for example. The nukes could’ve created some previously unknown effects in the atmosphere. The study also says the flashes could have been metallic objects far above our planet – perhaps even visitors from other worlds. But many scientists say we need a much more thorough look at the pictures before we’ll know what caused these flashes in the night sky. Script by Damond Benningfield

Long-term missions to the Moon and Mars will need a good understanding of the machines, the environment – and the people. Friction among crew members could make a mission much less productive – or even endanger lives. To minimize the risk, scientists are trying to understand how people get along during long periods of isolation. They’ve conducted test runs in laboratories. They’ve set up habitats on volcanoes and remote islands. They’ve studied research bases in Antarctica. And they’ve sent volunteers into the oceans. As with space travel, an undersea habitat is isolated and cramped, and the environment can be deadly. So it’s important for the crew to get along. NASA has conducted quite a few underwater expeditions. For many of them, astronauts spent a few days or weeks in a habitat off the coast of Florida. They conducted experiments both inside and outside the lab. They tested equipment and techniques that might be used in space. And scientists checked out how well they worked as a team. Recently, the European Space Agency sent 25 volunteers on a two-month trip aboard a submarine. Scientists used questionnaires to check on the volunteers. They also took samples of hair and saliva. The results helped track stress markers, changes in the immune system, and other reactions – better understanding the human factor in long-term missions to other worlds. Script by Damond Benningfield

If you stepped off a spacecraft onto the surface of Titan, you might experience a little dŽjˆ vu. Saturn’s largest moon has many of the same features as Earth. That includes rivers and seas, clouds, and even rainfall – it’s the only world in the solar system other than Earth with bodies of liquid on its surface. What wouldn’t seem familiar is the temperature – almost 300 degrees below zero Fahrenheit. In that icebox, water is frozen as hard as granite. So Titan’s rivers and seas and clouds are made of liquid methane and ethane. Titan is a large world – about half-again the diameter of our moon. And it has the densest atmosphere of any moon in the solar system; the surface pressure is equivalent to a depth of 50 feet in Earth’s oceans. The methane and ethane are quickly broken apart by sunlight, so the supply in the air has to be renewed. The most likely source is cryo-volcanoes – volcanoes that belch frozen water. Methane mixed with the water would waft into the atmosphere. The volcanoes could be fed by an ocean of liquid water below the surface – perhaps much more water than in all of Earth’s oceans combined. Both the ocean and the liquid bodies on the surface are possible homes for microscopic life – one more similarity to our own world. Saturn looks like a bright star near the Moon this evening. Through good binoculars or a small telescope, Titan looks like a tiny star quite near the planet. Script by Damond Benningfield

The planet Mercury is putting in a decent appearance in the evening sky now. It looks like a bright star low in the west during twilight. And tonight it has a prominent companion: the crescent Moon. In fact, they’ll look like they’re almost touching each other. Mercury is tough to see because it’s the closest planet to the Sun. Because of that, it never moves far from the Sun in our sky. At best, it’s visible for an hour or two after sunset or before sunrise. Right now, it’s farthest from the Sun in the evening sky. For a few nights, it won’t set until about an hour and 20 minutes after sunset. As twilight begins to fade, though, it’s so low in the sky that you’ll need a clear horizon to spot it. The Moon is just a day and a half past “new,” when it crossed between Earth and the Sun. So the Sun illuminates only a tiny fraction of the lunar hemisphere that faces our way. The rest of the disk will be faintly highlighted by earthshine – sunlight reflected from Earth. That will enhance the beauty of this duo in the fading twilight. Two other planets are close by. Saturn is to the upper right of Mercury and the Moon, and looks like a fairly bright star. Venus is heaving into view below them. It’s much brighter than Mercury, but much lower, making it tougher to pick out. But Venus will climb higher over the coming weeks – blazing as the “evening star.” More about the Moon and Saturn tomorrow. Script by Damond Benningfield

Car wrecks aren’t all alike, so there’s a wide range in the results. The same principle may apply to the bodies of the early solar system, when the planets were taking shape. In fact, a recent study says the modern appearance of the planet Mercury could be explained by a glancing blow between two bodies of similar size. Mercury is an oddball among the rocky planets of the inner solar system. Its metallic core accounts for about 70 percent of its mass – a far higher ratio than for Earth or the other planets. And the core is surrounded by a fairly thin mantle – a layer of lighter-weight rocks. Some simulations have suggested that was the result of a giant impact – a massive collision between bodies of much different sizes. Such impacts were common in the early solar system; one of them might have led to the creation of the Moon. But the recent study suggested something else. It found that a glancing blow between Mercury and a similar-sized planet could have stripped away much of Mercury’s mantle. But the research doesn’t tell us what happened to the other planet, or the debris from the impact. So scientists will ponder the possible collision a little longer to understand the planet Mercury. Mercury is peeking into view in the early evening. It looks like a bright star, but it’s quite low in the west during twilight, so it can be hard to spot. The Moon will join it tomorrow night; more about that tomorrow. Script by Damond Benningfield

There’s nothing like a merger to stir things up. That applies not only to companies and families, but to galaxies as well. One example is Messier 61. A recent merger with a smaller galaxy has brought its central black hole to life, triggered the birth of thousands of new stars. It also kicked out a ribbon of stars that’s as long as the galaxy itself. Messier 61 is a lot like our home galaxy, the Milky Way. It’s about the same size and mass, and it looks about the same – a beautiful spiral with a long bar of stars across its middle. But a close look shows big differences. M61 is giving birth to stars at a much faster rate than the Milky Way. It’s produced more supernovas – the explosive deaths of young, massive stars. The supermassive black hole in its heart is “feeding” much more voraciously. And last year, astronomers discovered a “streamer” of stars behind M61. The streamer is a hundred thousand light-years long, and ten thousand wide. The likely cause of all that activity is a merger with a smaller galaxy. The encounter squeezed big clouds of gas, triggering the starbirth. It provided fresh material for the black hole. And it pulled out stars in the galaxies to form the long tail – stirring things up in a beautiful spiral galaxy. M61 is 55 million light-years away, in Virgo. It climbs into the sky in mid-evening, and sails high across the south later on. It’s an easy target for binoculars. Script by Damond Benningfield

A celestial grandfather strolls low across the south on winter evenings. He’s represented by two stars. In the western world, they’re part of the constellation Columba, the dove. But in ancient China they were known as the Grandfather. The stars are Alpha and Epsilon Columbae. Coincidentally, they’re about the same distance from Earth – about 280 light-years. And both are much bigger and brighter than the Sun. But there’s a big difference in their ages, so the stars aren’t related. Alpha – the First Star of Grandfather – is the brighter of the two – the brightest member of Columba. It’s less than a hundred million years old – about two percent the age of the Sun. But it won’t be around much longer. It’s about four and a half times the mass of the Sun. Heavier stars age more quickly. In the next 150 million years or so, Alpha will move out of the “prime” phase of life and into the next phase, as a giant. Epsilon has already reached that phase. It’s not as massive as Alpha, but it’s about one and a half billion years older – a third the age of the Sun. It’s puffed up to many times the size of the Sun, so it shines much brighter. Before long, though, it will cast off its outer layers, leaving only its hot, dead core – and Grandfather will be down to a single star. Columba is low in the south-southeast at nightfall. Alpha and Epsilon are close together, near the center of the constellation. Script by Damond Benningfield

On summer nights, Earth faces the heart of the Milky Way Galaxy. That part of the Milky Way features dense clouds of stars. Under dark skies, it’s quite a sight. But during the long, cold nights of winter, we’re facing the opposite direction – toward the galaxy’s edge. So the Milky Way looks thin and faint – a bare ghost of its summer glory. No matter which direction you face, the hazy band of light known as the Milky Way represents the combined glow of millions of stars that outline the galaxy’s disk. The disk is about a hundred thousand light-years wide, but only a few thousand light-years thick. It contains a few hundred billion stars. The center of the galaxy is densely packed, like the downtown of a major city. But its outskirts are like the suburbs. There are fewer stars, and they’re more widely spread. And the closer to the galaxy’s edge, the more thinly spread the stars become. The Milky Way doesn’t end at the edge of the disk. The disk is surrounded by a “halo” of stars and dark matter. It extends hundreds of thousands of light-years into space in every direction. But the halo is like the countryside – a few solitary residents spread far and wide. So nothing in the halo is visible without a good telescope – far outside the galaxy’s disk. The Milky Way arcs high across the sky on February evenings. You need nice dark skies to see it – the thin but still beautiful glow of our home galaxy. Script by Damond Benningfield

If you walk under a ladder after breaking a mirror, does that make your day doubly unlucky? Since we’re a science program, we’ll say no. But that double-trouble philosophy underpins the superstitions about Friday the 13th. Both Friday and the number 13 have been considered bad luck. Put them together, and you have what may be the most feared of any day-and-date combo. The individual superstitions both have religious and mythological origins. In Christianity, for example, the Last Supper was shared by 13 men. And Jesus was crucified on a Friday. Just when the two were put together isn’t clear. The idea of Friday the 13th being unlucky shows up in some publications in France in 1834. The first record of it in the United States dates to 1882. How many people fear the date isn’t clear, either. But scientists have come up with a couple of names for it. The shorter one, believe it or not, is friggatriskaidekaphobia. Frigg was the Norse goddess for whom Friday is named, and triskaidekaphobia is fear of the number 13. Other than some unlucky teens in the “Friday the 13th” movies, there’s no evidence that the day is any more dangerous than any other. A study in 2011 compared hospital records for 13 Fridays the 13th to other date combinations. There was no bump in the number of emergency-room visits – nothing unlucky about Friday the 13th. Script by Damond Benningfield

The surface of Ariel looks like a sheet of paper that’s been loosely crumpled. It’s covered with ridges, wrinkles, and gashes. That may be telling us that Ariel once had a deep ocean of liquid water. Ariel is one of the larger moons of the planet Uranus. It’s about 720 miles in diameter – a third the size of our moon. It orbits just a hundred thousand miles from the planet – much closer than the Moon is to Earth. It’s roughly a 50-50 mix of ice and rock. Our only good look at Ariel came in 1986. Voyager 2 flew past it and photographed about a third of its surface. The pictures revealed a complex face. It has a mixture of old and young craters, deep ridges, and smooth plains that might have been paved by water gurgling up from inside the moon. A recent study modeled the orbit of Ariel over the ages. It found that the orbit was once much more lopsided than it is today. As Ariel moved in and out, the gravity of Uranus stretched and squeezed the little moon. That could have melted some of the ice inside it, creating an ocean a hundred miles deep, topped by a thin crust of ice. The stress of all the stretching and squeezing could have cracked the ice, creating the wrinkly surface we see today. Uranus is high overhead at nightfall. It’s below the Pleiades star cluster, and farther to the right of the bright orange star Aldebaran. Through good binoculars, the planet looks like a faint star. Script by Damond Benningfield

Ursa Major III is doomed. It’s falling apart, and may vanish completely in a couple of billion years. There’s not much to it even now. It’s so faint that it wasn’t discovered until 2023. It contains about 60 stars – all of them ancient, and all much smaller and fainter than the Sun. They add up to only about 16 times the Sun’s mass. They’re packed into a loose ball about 20 light-years wide. But the total mass is about 2,000 times greater than the mass of the visible stars. That’s led to some confusion about its nature. One idea is that it’s a small galaxy that’s orbiting the Milky Way. Most of its mass would consist of dark matter – matter that produces no energy, but that reveals its presence through its gravitational pull on the visible matter around it. A study last year suggested a different nature – a star cluster held together by a clump of black holes. The cluster might have been born with a hundred thousand stars or more. When some of the stars died, they formed black holes, which congregated near the cluster’s middle. The gravity of the Milky Way pulled away many of the cluster’s stars. Encounters with the black holes kicked out many more. And the study says the cluster will fall apart completely in about two billion years. The cluster – or galaxy – is about 30,000 light-years away, in the great bear. But Ursa Major III is far too faint to see, even with a telescope. Script by Damond Benningfield

Stars are born from huge clouds of gas and dust. Many of the stars remain close together, forming clusters. But as a cluster moves through the Milky Way, it gets pulled apart. The gravity of the rest of the galaxy tugs away the stars on the outskirts of the cluster. It also loosens the rest of the cluster, making it easier to pull away more stars. A recent study looked at how that’s played out in the region around the Pleiades cluster. Using telescopes in space and on the ground, researchers measured how fast the stars in the region are spinning. That provides a rough measure of their age – the younger the star, the faster it spins. They also measured the motions of the stars through the galaxy, allowing them to trace the paths of the stars far into the past. And they compared the compositions of the stars; stars that were born together are made of the same mixture of elements. From that, they found that the Pleiades and several smaller groups were close together tens of millions of years ago. That suggests they were born together before heading their separate ways. The study also found hundreds of stars between the groups that had belonged to one of the groups in the past. Today, the groups and loners are spread across 2,000 light-years of space – the Giant Pleiades Complex. Look for the Pleiades high overhead at nightfall. It looks like a tiny dipper – the heart of a once larger family of stars. Script by Damond Benningfield

Antares is a rare star. It’s one of the few named for what it’s not. The name is Greek. It combines “anti,” which means “against” or “opposed to” – with Ares – the Greek version of Mars, the god of war. So the name means “not Mars” or “rival of Mars.” It was given the name because its color is similar to that of Mars – bright orange. The color indicates that the surface of Antares is thousands of degrees cooler than the surface of the Sun. Cooler stars glow red or orange, while hotter stars are white or blue. Antares is one of many designations for the star. Because it’s the brightest star of Scorpius, it’s also known as Alpha Scorpii. And it’s also called the heart of the scorpion – Cor Scorpii. Antares also has designations in many catalogs – lists of stars that have something in common. It’s in the bright-star catalog as HR 6134. It has a companion star, so it’s in the binary-star catalog. And it’s in several catalogs of objects that produce a lot of infrared light. In all, Antares has dozens of names and catalog numbers – an impressive list for an impressive star. The gibbous Moon slips past Antares the next couple of mornings. The star will be to the left or lower left of the Moon at dawn tomorrow. And it will stand a little closer to the upper right of the Moon on Wednesday. Tomorrow: more stars for the Pleiades. Script by Damond Benningfield

Family members don’t always stay close together – they can be separated by thousands of miles. But one member of the Milky Way Galaxy’s family takes the separation to extremes. It’s 300,000 light-years from the center of the galaxy – one of the most distant residents of the Milky Way yet seen. NGC 2419 is a globular cluster – a group of about a million stars. They form a dense ball a few hundred light-years across. Any star near the middle of the cluster would have thousands of neighbors within a few light-years. Compare that to our own neighborhood – only three stars reside less than five light-years from the Sun. NGC 2419 is one of the Milky Way’s oldest family members. The cluster was born more than 12 billion years ago – not long after the galaxy itself. All of its big, bright stars burned out long ago. So almost all of the remaining stars are much less massive than the Sun. The cluster follows a highly stretched-out orbit around the center of the Milky Way. That’s led to suggestions that it was born elsewhere, then captured by the Milky Way. But there’s no confirmation of that idea. So NGC 2419 is still considered a far-away relative of the rest of the Milky Way. The cluster is in the uber-faint constellation Lynx, which is in the east-northeast at nightfall. NGC 2419 is an easy target for just about any telescope. Script by Damond Benningfield

Alpha Lyncis is only about a third of the age of the Sun. Yet the star has already zoomed through the prime phase of life. Now, it’s nearing the end of its life. And it’s letting us know about it – it’s the brightest star of the constellation Lynx. That’s not necessarily saying much. Lynx is a large constellation, but it’s faint – only a few of its stars are bright enough to see from light-polluted cities or suburbs. In fact, the astronomer who created it, in the 1600s, called it “Lynx” because you needed the eyes of one to see it. Alpha Lyncis is classified as a red giant. It’s about half-again the mass of the Sun. Heavier stars age more quickly. Such a star “burns” through the original hydrogen in its core in a hurry. As the core adjusts to the change, the star’s outer layers puff up. Today, Alpha Lyncis is more than 50 times the diameter of the Sun. As it got bigger, the star got cooler and redder – making it a red giant. Puffing up also made the star hundreds of times brighter than the Sun. So Alpha Lyncis is visible – faintly – even though it’s a little more than 200 light-years away. That makes it one of the few stars in this faint constellation that you don’t need the eyes of a lynx to see. Lynx is well up in the east-northeast at nightfall. It’s about half way between the Big Dipper and the twins of Gemini. But you need nice, dark skies to see much. More about the constellation tomorrow. Script by Damond Benningfield

The Moon snuggles close to the bright star Spica late tonight. They climb into good view by about midnight, and are high in the sky at dawn. At their closest, they’ll be separated by just a couple of degrees – about the width of your finger held at arm’s length. That closeness is just an illusion – the Moon and the star are separated by a vast gulf. The Moon is our closest neighbor. Tonight, it’s a little less than a quarter of a million miles away. At that distance, sunlight reflecting from the lunar surface takes about one and a third seconds to reach Earth. That means we see the Moon as it looked one and a third seconds earlier. The Moon is moving farther from us – by an inch and a half per year. That’s a result of the tides. Earth and Moon exert a gravitational grip on each other. That slows Earth’s rotation, making the days a little longer. To balance the books, the Moon moves farther away. Spica is more than nine billion times farther than the Moon. Its light takes about 250 years to reach Earth – the star is 250 light-years away. So as you look at Spica tonight, you’re actually seeing the bright star as it looked 250 years ago – about the time of the American Revolution. And it’s moving away as well – by about 60 million miles per year. That’s a result of Spica’s motion around the center of the galaxy – an orbit that’s carrying the brightest star of Virgo into the distance. Script by Damond Benningfield

The star cluster M79 is messy. It’s shedding some of its stars, creating a “tail.” Over the eons, in fact, the cluster might have lost most of the stars it was born with. Messier 79 is a globular cluster – a ball-shaped family of about 150,000 stars. The cluster is more than 11 billion years old, so its stars are among the oldest in the entire Milky Way Galaxy. There’s a trail of stars behind the cluster. The stars probably were stripped away by the gravity of the rest of the galaxy – especially its dense core. Today, M79 is about 42,000 light-years from the Milky Way’s heart. But its orbit might bring it within just a few hundred light-years of the center. At that distance, the gravity of the galaxy’s core overpowers the gravity of the cluster. So stars in M79’s outskirts are pulled away. Eventually, they move away, and follow their own paths across the galaxy. Some simulations have suggested that M79 has lost up to 85 percent of its original population of a million stars or so. And every future passage through the heart of the galaxy will pull away more stars – leaving only a glimmer of M79’s original glory. M79 is in Lepus, the hare. The constellation is close to the lower right of bright Orion, in the southeast at nightfall. M79 is below the outline of the rabbit. You need binoculars to pick it out. Script by Damond Benningfield